1. Field of the Invention
The general inventive concept described herein through illustrative embodiments thereof relates to optimizing a write current in a data storage device, and more particularly, to a method and apparatus to determine optimal parameters for a write current while taking the pole tip protrusion (PTP) of a magnetic head into consideration.
2. Description of the Related Art
Conventionally, hard disk drives (HDDs), which are data storage devices, were originally used in computer systems to read data from and write data to a disk using a magnetic head. In recent years, however, HDDs are found in a wide variety of applications, such as digital video recording equipment and personal media players.
In HDDs, a typical magnetic recording head is made of metal and a slider supporting the magnetic head is made of a non-metallic material. When a write current flows through a metal coil of the magnetic head, a magnet flux is generated for writing data on a suitable disk. Also, since the coil includes a finite resistance, the write current flowing through the coil generates Joule heat. As a consequence of the generated heat and a difference between the coefficients of thermal expansion of the magnetic head made of metal and the slider made of the non-metallic material, the structure forming a pole of the magnetic head is caused to protrude. Such a phenomenon is referred to as “pole tip protrusion” (PTP).
In general, there is a difference in temperature between a point in time when a write operation starts and a point in time when the write operation ends. That is, since the temperature of the magnetic head at the time when the write operation starts is lower than the temperature of the magnetic head at the time when the write operation ends, the amount of PTP at the time when the write operation starts is less than that at the time when the write operation ends.
Due to the variance in the amount of PTP over time, a space between the magnetic head and a disk, referred to herein as the “flying height,” is not constant. If the flying height of the magnetic head decreases to less than a lower limit, the magnetic head and the disk may collide with each other, thereby resulting in damage to one or both of the magnetic head and disk and/or overheating the magnetic head to render it at least temporarily inoperative, which is a condition known in the art as thermal asperity (TA). On the other hand, if the flying height of the magnetic head is greater than an upper limit, the magnetizing force at the surface of the disk may be diminished to the point where it is difficult to properly write data.
In particular, thermal PTP (TPTP) of the magnetic head when the write operation starts is generally at a minimum, which may lead to poor initial recording quality if the magnetic flux during the write operation has been optimized to a flying height corresponding to when TPTP has occurred.
To solve these and other problems, the present applicant has disclosed Korean Patent Application No. 2002-79751, filed on Dec. 13, 2002, entitled “Method of Measuring TPTP of Magnetic Head and Method of Controlling Write Current Thereof.”
Although a method of measuring the TPTP of a magnetic head is explained in detail in the cited reference, a method of precisely determining a PTP control duration over which an overshoot amplitude of a write current is controlled has not been developed. Consequently, the “overshoot value” of the write current, i.e., the peak amplitude of the write current during the write operation, cannot be effectively controlled considering PTP.
Thus, as higher capacity, higher density, and smaller HDDs are developed, there is a demand for a precise method of determining a PTP control duration over which a PTP control signal controls an overshoot amplitude of a write current considering PTP.